diff options
Diffstat (limited to 'gcc/tree-ssa-dom.c')
| -rw-r--r-- | gcc/tree-ssa-dom.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c index b007388..5376ff9 100644 --- a/gcc/tree-ssa-dom.c +++ b/gcc/tree-ssa-dom.c @@ -1731,9 +1731,26 @@ cprop_into_stmt (gimple *stmt) { use_operand_p op_p; ssa_op_iter iter; + tree last_copy_propagated_op = NULL; FOR_EACH_SSA_USE_OPERAND (op_p, stmt, iter, SSA_OP_USE) - cprop_operand (stmt, op_p); + { + tree old_op = USE_FROM_PTR (op_p); + + /* If we have A = B and B = A in the copy propagation tables + (due to an equality comparison), avoid substituting B for A + then A for B in the trivially discovered cases. This allows + optimization of statements were A and B appear as input + operands. */ + if (old_op != last_copy_propagated_op) + { + cprop_operand (stmt, op_p); + + tree new_op = USE_FROM_PTR (op_p); + if (new_op != old_op && TREE_CODE (new_op) == SSA_NAME) + last_copy_propagated_op = new_op; + } + } } /* Optimize the statement in block BB pointed to by iterator SI |